Through-insulation welding method and apparatus

ABSTRACT

A weld is made between an insulated wire and a terminal by pressing the wire against the terminal with an electrode, applying ultrasonic vibrations to the electrode to scrub away insulation so that electrical contact is made between the central conductor of the wire and both the terminal and electrode, and then applying a welding current through the electrode to flow through the wire and terminal to weld them together.

United States Patent 11 1 1111 3,789,183 Conle Jan. 29 1974 y [54]THROUGH-INSULATION WELDING 2,946,l 19 7/ 1960 Jones et a1. 219/86 XMETHOD AND APPARATUS 3,272,960 9/1966 Smith 219/92 X 3,350,582 10/1967Attwood et al.. 3l0/8.3 X [75] Inventor: Larry C y, Fountaln y,3,524,083 8/1970 Last et a1 3l0/8.7 x Calif. 3,357,090 12/1967 Tittany29/4975 3,673,681 7 1972 St k 219 119 X [73] AS51811: Accra'plmt f'cm'lmahm 3,578,940 5/1971 21 9/92 x Santa Ana, Callf.

[22] Filed: Feb. 28, 1973 Primary Examiner-Bruce A. Reynolds 1 pp NO:336,811 Attorney, Agent, or Fzrm-L1ndenberg, Fre1l1ch &

Wasserman [52] US. Cl 219/92, 29/4975, 219/78,

219/86, 219/119, 3l0/8.1 [57] ABSTFACT [51] Int. Cl B23k 11/14 A Weld IS9 en n Insulated wire and a term- [58] Field of Search. 219/92,78, 86,118, 119, 233, ml by Pressmg the Wlre agamst the fermlnal Wlth an219/91; 29/1316 46, 75 3 310/8, electrode, applying ultrasonicvibrations to the elec- 82, 83, 7 trode to scrub away insulation so thatelectrical 1 contact is made between the central conductor of the 56]Reference5 Cited wire and both the terminal and electrode, and thenapplying a welding current through the electrode to flow UNITED STATESPATENTS through the wire and terminal to weld them together. 3,614,37510/1971 Becker 219/91 3,519,782 7/1970 Mallery 219/78 14 Claims, 8Drawing Figures (/1 TFIIUIV/C 7 41- 68 6/4 Z2 DP/Vfl? 52 [/,?([//7 I 1i047 Pffli! M 76 W rfW/fffl 77 l I I I0 2 I 4'6 c L2 75 44 g l :0 T "2%?l (WI/7W2 ,4 29915;;

.96 9 l 10 I; f ,e X

Ill/I171! 16 k4,? 22 J4 12 .98 f1 [l /"55b: M/ 0 Maw/xv! fl/P/V' 102Pan/5? z/pfizl PATENTH] JAN 2 9 E974 SHEET 1 0F 2 PAIENT JAN29 i974 P1?Viz? SHEET 2 OF 2 THROUGH-INSULATION WELDING METHOD AND APPARATUSBACKGROUND OF THE INVENTION This invention relates to methods andapparatus for welding an insulated wire to a terminal.

Complex electronic assemblies often include large numbers of closelyspaced miniature terminals which must be electrically interconnected.Such interconnections can be made using continuous wires that are weldedat various points therealong to the different terminals. Insulated wiresare generally employed, and therefore apparatus must be provided to formwelds through the insulation to connect the central conductor of thewire to the terminal.

One method which has been used for throughinsulation welding includespressing a welding electrode against the insulated wire to force itagainst the terminal with enough force to rupture the insulation. Suchcold deformation of the insulation establishes electrical contactbetween the central conductor of the wire and both the terminal andelectrode. Welding current is then passed through the electrode andthrough the wire and terminal to weld the wire to the terminal. In atypical machine that employes this method, the electrode is rapidlylowered against the wire so that the electrode punches through theinsulation. As soon as the force on the electrode reaches apredetermined level which has been found sufficient to assurebreakthrough of the insulation, a welding current supply isautomatically turned on. The insulation-rupturing force for many wiresis relatively large such as at a level of ten pounds, while the weldingforce for the wire must be at a lower level such as three and one-halfpounds in order to form a good weld. Such a welding technique isdescribed in US. Pat. Nos. 3,596,044 and 3,627,970. This method ofwelding has the disadvantage that it works well only for insulationwhich readily ruptures at moderate pressures, such as type FEP Teflon(fluorethylene propylene). Many other types of insulation which aretougher and which exhibit better cut-through resistance, such as typeTFE Teflon, Tef-Zel, Kynar, and polyurethanes, do not readily rupture,and-the above welding technique does not work well with theseinsulations.

SUMMARY OF THE INVENTION In accordance with one embodiment of thepresent invention, an apparatus and method is provided for weldinginsulated wires to terminals, which is readily usable for a wide varietyof insulation materials and which produces welds of a consistent highquality when used with either the easily ruptured or tougher insulationmaterials. The weld-forming method includes pressing a welding electrodeagainst an insulated wire to press the wire against a terminal, andapplying vibrations to the electrode. The vibrations scrub awayinsulation around the central conductor of the wire, to establish anelectrical connection between the central conductor and both theterminal and electrode. Welding current is then passed through theelectrode to flow through the central conductor of the wire and theterminal to weld them together. The force with which the electrode ispressed against the wire during the scrubbing is generally lower thanthe force required to statically rupture the insulation, and in fact,this force may be the same as the force applied during the flow ofwelding current.

The novel features of the invention are set forth with particularly inthe appended claims. The invention will best be understood from thefollowing description when read in conjunction with the accompanyingdrawmgs.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partially side elevationand partially block diagram view of a welding system constructed inaccordance with the present invention;

FIGS. 2A-2C are magnified sectional views of the tip region of thewelding electrode assembly of FIG. 1, showing several stages in thewelding method of the invention;

FIG. 3 is a sectional view taken on the line 3--3 of FIG. 2B.

FIG. 4 is a partial sectional view of a welding head assemblyconstructed in accordance with another embodiment of the invention;

FIG. 5 is a partial perspective view of a welding head assemblyconstructed in accordance with still another embodiment of theinvention; and

FIG. 6 is a partial perspective view of a welding head assemblyconstructed in accordance with yet another embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates a weldingsystem of the invention which includes a pair of opposed electrodes l0,12 that are used to weld regions of a continuous wire 14 to pinliketerminals 16 of a circuit assembly 18. The system includes upper andlower drives 20, 22 for moving the electrodes vertically against the pin16, and a transducer 24 for vibrating the upper electrode 10. Anoscillator, or ultrasonic driver 26 generates electrical currents thatenergize the transducer 24, while an acoustical horn 28 transmitsvibrations from the transducer to an electrode holder 30 to vibrate theelectrode. The ultrasonic vibrations remove insulation of the wire toprovide a path for welding current through the central conductor of thewire 14. Welding current is applied by a welding power supply 32 to thetwo electrodes 10, 12 to apply a voltage or potential between them, sothat current can flow between the central conductor of the wire 14 andthe terminal 16 to weld them together.

FIGS. 2A-2C illustrate various steps in the welding process of theinvention. FIG. 2A illustrates a first step, which includes pressing theupper electrode 10 against the insulated wire 14 topress the wireagainst the terminal 16. The wire 14 includes a central conductor 34 ofa weldable electrically conductive material such as a nickel alloy, anda layer of insulation 36 surrounding the conductor. The electrode 10 ispressed down with a force F which is normally less than the forcerequired to cold flow or rutpure the insulation 36 even in the case ofinsulation material that can be ruptured by a moderately high force.

FIG. 23 illustrates a next step in the process, which includes applyingvibrations, indicated by arrow V, to the electrode 10. The vibrationsare applied at a sufficient intensity and for a sufficient time to scrubaway a region of the insulation 36 which lies directly under theelectrode 10. The force F is maintianed during the application of thevibrations in order that the electrode can effectively scrub away theinsulation. The insulation is scrubbed away not only between theelectrode 10 and the conductor 34 of the wire, but also between theconductor 34 and the terminal 16. It is believed that the electrode 10first scrubs away insulation between it and the conductor 34, and thatthe electrode 10 then vibrates the conductor 34 so that the vibratingconductor scrubs away the insulation between it and the terminal 16 atthe region where it presses the insulation against the terminal. Theelectrode 10 does not press hard against any other regions of the wire,and therefore there is no damage to an region of the insulation otherthan the region directly under the tip of the electrode 10. Asillustrated in FIG. 3, the insulation portions 36a that are protectedfrom compression by the central conductor are normally not removed; onlywhere the central conductor faces the electrode and terminal isinsulation removed. As a result of the vibrations during the applicationof the downward force, the central conductor 34 of the wire directlycontacts both the terminal 16 and the electrode 10.

FIG. 2C illustrates a next' step in the process, which involves applyinga welding current, indicated by arrow 1, through an electrode 10 to flowthrough the central conductor 34 and terminal 16. This current isapplied while the downward force F is applied on the electrode 10 topress it against the wire and to press the wire against the terminal 16.The current 1 forms a weld 38 between the conductor 34 and terminal 16.After the weld has been formed, the electrode 10 is lifted and moved toa position over another terminal of the circuit board assembly to weldthe wire 14 to that terminal.

Referring again to FIG. 1, it can be seen that the welding systemincludes various circuits and controls for performing the weldingmethod. An operator begins a welding cycle by depressing a foot pedalswitch 40 to move a switch member 42 thereof from an initial positionillustrated in the figure into contact with a switch contact 44. Theswitch 40 that carries current from a control current source 46 to atimer circuit 48. The foot pedal switch has another switch member 49that moves in unison with the switch member 42, to connect the currentsource 46 to a contact 51. As soon as the foot pedal switch isdepressed, the contact 51 delivers a current through line 50 to theelectrode drives 20, 22, to raise the lower electrode 12 and lower theupper electrode 10 towards theterminal 16. The upper drive 20 includes asolenoid 54 which pulls down a plunger 56 againstthe force of a spring58 to permit an electrode assembly holder 60 to move down. A spring 62constantly presses down the holder 60 with an accurately known force, sothat the assembly 30 and upper electrode 10 thereof are pressed downagainst the terminal 16 with a closely controlled force.

A brief time after the electrode drives have been energized, the timercircuit 52 applies a current through its output 52 to the ultrasonicdrive 26 to turn it on for a brief time period. The ultrasonic drive 26than generates a high frequency current that is delivered to thetransducer 24 to energize it. The transducer 24 includes a pair ofcrystals 64, 66 of the type that vibrates at a large amplitude whencurrents are applied thereto, such crystals as those of lead zirconatetitanate being suitable for this purpose. The vibration assemblyincludes a contact washer 68 located between the crystals and a pair ofend contacts 70 connected to the crystals. The contact washer 68 isconnected through a line 72 to an output of the ultrasonic driver 26,while the contacts are connected through a line 74 to ground. Theultrasonic drive 26 has another output connected through a line 76 andswitch 77 to ground, the switch 77 having a contact 78 and a switchmember 80 that lead to ground potential. When the drive 26 is on, thetransducer 24 vibrates the solid metal acoustic amplifier cone 28 thatleads to the electrode holder 30. The cone 28 is dimensioned to providea large amplitude of vibrations at the holder 30 so that the electrode10 is vibrated at a considerable amplitude to scrub the insulation offthe wire.

As mentioned above, the operator first depresses the foot pedal switch40 to move the switch members 42 and 49 and thereby lower the upperelectrode 10 and apply vibrations thereto. The foot pedal switch 40 isof a type which can be depressed hard to cause the switch member 42 tomove out of engagement with contact 44 and into engagement with anothercontact of the switch assembly. (The other switch member 49 remainsengaged with its contact 51 even when the foot pedal is depressed hard).This hard depression of the foot pedal results in current from thesource 46 flowing through the contact 90 to a relay coil 92 that movesthe switch member 80 and another switch member 94. Movement of theswitch member 80 out of engagement with contact 78 that leads to theultrasonic driver 26, results in isolation of the driver 26 from groundpotential to protect it from welding currents. Movement of the otherswitch member 94 brings it into engagement with a contact 96 to completea circuit through a pair of control terminals 98 of the welding powersupply 32 to turn it on. The welding power supply 32 than supplies awelding potential between its outputs 100, 102 that are respectivelycoupled to the upper and lower electrodes 10, 12.

When the welding power supply is turned on, an electrical circuit hasalready been completed through the electrode 10, the central conductorof the wire 14, the terminal 16, and the lower electrode 12, so thatwelding current can flow to weld the conductor to the terminal. Thewelding power supply 32 includes a current regulator and timer (notshown) that provides a level of welding current for a time period thatwill produce a good weld, and thereafter no welding current is applieduntil the next time that the starting terminals 98 are interconnected.

The time period during which the electrode 10 is vibrated to scrub awayinsulation on the wire, and the time period which welding current isapplied to the electrodes are normally a fraction of a second each, forthe welding of small wires .typically used in the construction ofcircuit board assemblies. For example, ultrasonic vibrations may beapplied to the electrode 10 at a frequency of 50 kHz for a period of 100milliseconds, followed by the application of welding current for aperiod such as three milliseconds, while maintaining a constant downwardfP rce of 4 /2 pounds on the electrode 10. The operator can depress thefoot pedal switch 40 with a low pressure and then a greater pres-' sureto complete the vibration and welding, and she may then release the footpedal switch. A control can be provided so that the operator merelydepresses a foot pedal switch with one pressure, and the vibration andwelding steps are automatically performed in sequence. After theoperator releases the foot pedal switch, she depresses a button (notshown) that operates a numerically controlled positioning device (notshown) that repositions the circuit board assembly 18 to move a nextterminal thereof under the electrode 10. During such movement of thecircuit board assembly 10, the wire 14 is payed offa reel 104, so that acontinuous length of wire may be welded at many locations to terminalsof the circuit board.

In constructing the apparatus that vibrates the eletrode and then passeswelding current through it, care must be taken to prevent damage to theultrasonic driver 26 from welding current. The switch assembly 77,including the relay 92 thereof, prevents welding current from flowingthrough the ultrasonic driver, by automatically disconnecting the driver26 from ground prior to turning on the welding power supply 32.

The factors that must be considered in scrubbing off wire insulationinclude the frequency of the vibrations, the amplitude of vibrations atthe electrode 10, the pressure of the electrode 10 against the wire, andthe type of insulation. The equipment often can be simplifled byutilizing the same force during scrubbing of insulation as is requiredfor welding, so that it is not necessary to provide equipment forpressing down the electrode at two different pressures or to alternatebetween the pressures at different times in the cycle of operation.Also, an ultrasonic driver 26 with a constant frequency and outputamplitude may be utilized with only the time period being varied. Thetime period during which vibrations are applied should not be too long,or else the central conductor 34 of the wire may be deformed. A widerange of vibration frequencies may be utilized, although frequencies onthe order of 50 kHz have been found to work well for small wires of thetype typically used in constructing circuit board assemblies.

The use of electrode vibration to remove insulation from a wire justprior to resistance welding permits through-insulation welding for awide range of insulation materials. A previous through-insulationwelding technique which utilizes only high pressure to rutpure theinsulation was useable only with cold flowable material such as type FEPTeflon. The present vibration technique can be utilized with insulationmaterials such as type TFE Teflon, Tef-Zel, Kynar, and polyurethanes,which are tougher and exhibit better abrasion and cutthrough resistancethan type FEP Teflon. The vibration or scrubbing action at the weldingtip also has the important advantage that itremoves oxide particles andsolvent residue from the welding interfaces, thereby producing moreconsistent welds. In previous throughinsulation techniques whichutilized only high pressure to rupture the insulation, the weld qualitycould be seriously affected by particles of foreign material thathappend to be present at the welding interfaces and which would not bedisplaced merely by high pressure.

The use of electrode vibration also has been found to produce good weldsover a wider range of welding power inputs, than has been possible forthe previous method which utilized a high initial force to rupture theinsulation. This is important because common power supplies such as thecapacitor discharge type provide a variable output due to aging of thecapacitor and incomplete regulation of line voltage. It is believed thatthe vibration method produces good welds even at the low range ofsettings on the power supply because vibrations produce a moreconsistently low resistance along the current path, and that good weldsare produced even at the high range of settings on the power supplybecause the absence of a high insulationrupturing pressure reduces thepossibility of damage to the central conductor of the wire that canoccur during insulation removal.

Thus, the method and apparatus of the present invention not only permitsthe application of throughinsulation welding to a wider range ofinsulation materials, but produces more consistent welds for all typesof insulation and over a wider range of welding power supply outputs. Inaddition, the technique eliminates the need to provide an initial veryhigh pressure for rupturing insulation, so that both removal ofinsulation as well as resistance welding can be performed at moderateforces, and in fact may be performed at the same force level to simplifythe equipment. It is possible to change the downward force on theelectrode 10 between the vibrating step and the application of weldingcurrent, but it is desirable to avoid lifting the electrode entirely offthe wire before resistance welding to avoid the possibility thatcontaminating foreign material will be introduced at the weld point. Itshould be noted that while vibrations for scrubbing away the insulationare usually most easily applied through the resistancewelding electrode,it is possible to apply vibrations in other ways, as by vibrating theterminal.

FIG. 4 illustrates a welding head assembly constructed in accordancewith another embodiment of the invention, which provides a compactassembly for scrubbing and resistance welding. The assembly includes anelectrode of a material such as copper tungsten, with a centralpassageway 112 through which the wire 14 extends and a metal block 114of a material such as aluminum for holding the electrode. A washer l 16supports a transducer which includes a pair of crystals 118, and acontact washer 122 between them. A crystal cap 122' rests upon thecrystals. The cap 122', crystals, and block 114 all have central holes,and a bolt 124 extends through these holes and is threaded at its lowerend into the block 114 to hold the assembly together. The bolt 124 has acentral passage 126 through which the wire 14 extends to the electrode110. The washer 116 is threaded at its periphery to a holder 128 that isattached to a drive mechanism that raises and lowers the assemblyagainst and away from a terminal. An elastomeric O-ring 129 assures atight fitting of the washer 116 in the holder 128 while minimizing thetransfer of vibrations to the holder 128 so that a minimum of vibrationenergy is lost therethrough. A pair of leads 130, 132 connect to anultrasonic driver for providing currents to drive the crystal structure.Another lead (not shown) connects to the block 114 to supply weldingcurrents thereto. This assembly is compact and provides efficienttransfer of vibrations from the crystal structure to the electrode witha minimum of loss to other masses in the vicinity of the electrode.

FIGS. 5 and 6 illustrate welding head assemblies constructed inaccordance with further embodiments of the invention, wherein simplifiedmounting and efficient coupling of vibrations is achieved. In FIG. 5, anelectrode mount holds the welding electrode 142, and the mount issupported on a holder 144 by a vibration source 146. The vibrationsource includes a pair of crystals 148, separated by a conductive washer152. One crystal 148 is fastened by epoxy cement that contains copperfilings to the holder 144, while the other crystal 150 is fastened byepoxy cement containing copper filings to the electrode mount 140. Theholder 144 is a metal bar while the mount 140 is a metal member with aslot for receiving the electrode and a screw 154 for closing the slot toclamp the electrode in place. A crystal driver 156 applies current between the washer and the opposite crystal faces. A cable 158electrically connects the holder 144 and mount 140. A welding supply 160supplies welding current to the electrode 142 and another electrode. Theepoxy cement layers provide good mechanical coupling of the electrodeholder to the vibration source-as well as an electrical path. Thewelding head of FIG. 6 is similar to that of FIG. 5, except that thevibration source 162 produces horizontal vibrations instead of verticalvibrations. This is accomplished by using a holder 164 that holds thecrystals of the vibration assembly so they vibrate the electrode holder166 in a horizontal direction. The actual vibration mode at the tip ofthe electrode is difficult to predict, but either direction ofvibrations at the electrode holder can cause removal of insulation of awire that presses against the electrode tip.

The present invention therefore provides a method and apparatus forcreating welds between an insulated wire and a terminal, which can beemployed with a wide variety of wire insulation materials and whichproduces high consistent welds using equipment of minimum complexity.The method involves the application of vibrations to a resistancewelding electrode as it presses a wire against a'terminal, to cause thescrubbing away of insulation between the central conductor of the wireand both the terminal and electrode, and the application of weldingcurrent through the electrical path thus established to-weld the centralconductor of the wire to the terminal. The pressure employed during thescrubbing step is lower than that required to cold flow or rupture theinsulation in the absence of vibrations, and in fact, may be of the samelevel as the force used during the subsequent resistance welding step.The apparatus includes a vibration mechanism such as a crystaltransducer which is driven by an oscillator,

and the oscillator is protected from welding current by utilizing aswitch that automatically disconnects the oscillator from a groundpotential whenever the welding current supply is turned on. A variety ofvibration sources can be utilized, including magnetostrictive devicesand motor driven mechanical vibrators.

Although particular embodiments of the invention have been described andillustrated herein, it is recognized that modifications and variationsmay readily occur to those skilled in the art and consequently it isintended that the claims be interpreted to cover such modifications andequivalents.

What is claimed is:

1. A method for through-insulation welding to a terminal, of a wire thatincludes a central conductor which is surrounded by an insulator,comprising:

pressing the wire against the terminal with a resistance-weldingelectrode;

establishing vibrations at the region where the wire is pressed betweenthe electrode and the terminal to scrub insulation from the centralconductor at the locations thereof facing the electrode and terminal, sothe central conductor and terminal come into physical contact; and

flowing welding current in a series path through the electrode, centralconductor, and terminal while the electrode presses the centralconductor against the terminal, so that welding current flows betweenthe central conductor and terminal at the point where they are inphysical contact, to weld the cen tral conductor to the terminal.

2. The method described in claim 1 wherein:

said electrode is maintained pressed against said wire during the entireperiod between said step of establishing vibrations and said step offlowing welding current, whereby to prevent contamination prior toresistance-welding of the welding points that have been scrubbed clean.

3. The method described in claim 1 wherein:

said electrode presses at a substantially constant force level which isless that the force level required to rupture the insulation by pressurealone, during both said step of establishing vibrations and said step offlowing welding current.

4. The method described in claim 1 wherein:

said steps of establishing vibrations and flowing welding currentinclude energizing a transducer which is acoustically coupled to theelectrode and then establishing a welding potential between saidelectrode and a second electrode that contacts the terminal.

5. In a method of welding an electrical conductor which is coated withelectrical insulating material, to an electrically conductive terminalby means of a welding assembly which includes first and secondelectrodes, the steps comprising:

pressing at least the first electrode towards the terminal so that aportion of the insulation-coated conductor is caught between the firstelectrode and the terminal;

vibrating said first electrode while maintaining it pressed against theinsulation-coated conductor to remove the insulation so that theconductor establishes an electrical path between the first electrode andthe terminal;

establishing electrical contact between the second electrode and theterminal; and

applying a welding potential between the first and second electrodeswhile the second electrode is electrically coupled to said terminal andthe first electrode is maintained in electrical contact with theterminal through the wire.

6. The method described in claim 5 wherein:

said steps of vibrating and applying a welding potential are performedat the same force level of the first electrode towards the conductor.

7. The method described in claim 5 wherein:

said vibrating of said first electrode is terminated prior to theapplication of a welding potential between the electrodes.

8. Apparatus for through-insulation welding to an electrical terminal,of a wire that includes a central conductor and a covering of insulationthereabout, comprising:

an electrode with a tip; means for leading the wire across at least aportion of said tip; means for pressing the electrode towards a terminalso that the electrode presses the wire against the terminal;

means for creating vibrations at the region where the wire is pressedbetween the electrode and terminal to remove insulation at the locationsthereat where the central conductor faces the electrode and terminal;and

means for establishing a welding potential between said electrode andterminal to flow a current therebetween through said central conductor.

9. The apparatus described in claim 8 wherein:

said means for pressing maintains a constant pressure during operationof said vibration creating means and said means for establishing anelectrical potential.

10. Apparatus for welding a wire that includes an insulation-coveredelectrical conductor, to avterminal, comprising:

an electrode assembly including first and second electrodes; means forpressing said first electrode toward said terminal with said .wiretherebetween so the first electrode presses the wire against theterminal, and for moving said second electrode into electrical contactwith the terminal; means for vibrating said first electrode while itpresses the wire against the terminal to remove insulation on the wireand thereby establish an electrical connection between the firstelectrode and the terminal through the electrical conductor; and

power means for applying a welding potential between said electrodeswhile the first electrode presses the wire against the terminal and thesecond electrode is in electrical contact with the terminal, to flow awelding current through the electrical conductor and terminalv 11. Theapparatus describedvin claim 10 wherein:

said pressing means presses said first electrode toward said terminalwith a constant force during operation of said vibrating means and powermeans. 12. The apparatus described in claim 10 wherein: said vibratingmeans includes a transducer, an electrically conductive memberacoustically coupling the transducer to the first electrode, anoscillator, first and second signal conductors for connecting saidoscillator to said transducer, and a signal switch in series with saidfirst signal conductor; and

said power means includes a power switch which is closeable to applysaid welding potential between the electrodes: and including means forautomatically opening said signal switch prior to closing said powerswitch.

13. In a method of welding an electrical conductor which is coated withelectrical insulating material, to an electrically conductive terminalby means of a welding assembly which includes first and secondelectrodes, the steps comprising:

pressing at least the first electrode towards the terminal so that aportion of the insulation-coated conductor is caught between the firstelectrode and the terminal;

vibrating a ring-shaped transducer coupled to said first electrode whilemaintaining the first electrode pressed against the insulation-coatedconductor to remove the insulation so that the conductor establishes anelectrical path between the first electrode and the terminal;

applying a welding potential between the first and second electrodeswhile the second electrode is electrically coupled to said terminal andthe first electrode is maintained in electrical contact with theterminal through the wire; and

feeding the insulation-coated conductor through the ring-shapedtransducer.

14. Apparatus for through-insulation welding to an electrical terminal,of a wire that includes a central conductor and a covering of insulationthereabout, comprising: I

an electrode with a tip;

means for leading the wire across at least a portion of said tip,including walls forming a passageway in the electrode;

means for pressing the electrode towards a terminal so that theelectrode presses the wire against the terminal;

means for creating vibrations at the region where the wire is pressedbetween the electrode and terminal to remove insulation at the locationsthereat where the central conductor faces the electrode and ter minal,including a transducer with a central hole coaxial with said passagewayin said electrode acoustically coupled to said electrode, and anoscillator coupled to said transducer to drive it, said wire extendingthrough said hole in said transducer; and

means for establishing a welding potential between said electrode andterminal to flow a current therebetween through said central conductor.

1. A method for through-insulation welding to a terminal, of a wire thatincludes a central conductor which is surrounded by an insulator,comprising: pressing the wire against the terminal with aresistance-welding electrode; establishing vibrations at the regionwhere the wire is pressed between the electrode and the terminal toscrub insulation from the central conductor at the locations thereoffacing the electrode and terminal, so the central conductor and terminalcome into physical contact; and flowing welding current in a series paththrough the electrode, central conductor, and terminal while theelectrode presses the central conductor against the terminal, so thatwelding current flows between the central conductor and terminal at thepoint where they are in physical contact, to weld the central conductorto the terminal.
 2. The method described in claim 1 wherein: saidelectrode is maintained pressed against said wire during the entireperiod between said step of establishing vibrations and said step offlowing welding current, whereby to prevent contamination prior toresistance-welding of the welding points that have been scrubbed clean.3. The method described in claim 1 wherein: said electrode presses at asubstantially constant force level which is less that the force levelrequired to rupture the insulation by pressure alone, during both saidstep of establishing vibrations and said step of flowing weldingcurrent.
 4. The method described in claim 1 wherein: said steps ofestablishing vibrations and flowing welding current include energizing atransducer which is acoustically coupled to the electrode and thenestablishing a welding potential between said electrode and a secondelectrode that contacts the terminal.
 5. In a method of welding anelectrical conductor which is coated with electrical insulatingmaterial, to an electrically conductive terminal by means of a weldingassembly which includes first and second electrodes, the stepscomprising: pressing at least the first electrode towards the terminalso that a portion of the insulation-coated conductor is caught betweenthe first electrode and the terminal; vibrating said first electrodewhile maintaining it pressed against the insulation-coated conductor toremove the insulation so that the conductor establishes an electricalpath between the first electrode and the terminal; establishingelectrical contact between the second electrode and the terminal; andapplying a welding potential between the first and second electrodeswhile the second electrode is electrically coupled to said terminal andthe first electrode is maintained in electrical contact with theterminal through the wire.
 6. The method described in claim 5 wherein:said steps of vibrating and applying a welding potential are performedat the same force level of the first electrode towards the conductor. 7.The method described in claim 5 wherein: said vibrating of said firstelectrode is terminated prior to the application of a welding potentialbetween the electrodes.
 8. Apparatus for through-insulation welding toan electrical terMinal, of a wire that includes a central conductor anda covering of insulation thereabout, comprising: an electrode with atip; means for leading the wire across at least a portion of said tip;means for pressing the electrode towards a terminal so that theelectrode presses the wire against the terminal; means for creatingvibrations at the region where the wire is pressed between the electrodeand terminal to remove insulation at the locations thereat where thecentral conductor faces the electrode and terminal; and means forestablishing a welding potential between said electrode and terminal toflow a current therebetween through said central conductor.
 9. Theapparatus described in claim 8 wherein: said means for pressingmaintains a constant pressure during operation of said vibrationcreating means and said means for establishing an electrical potential.10. Apparatus for welding a wire that includes an insulation-coveredelectrical conductor, to a terminal, comprising: an electrode assemblyincluding first and second electrodes; means for pressing said firstelectrode toward said terminal with said wire therebetween so the firstelectrode presses the wire against the terminal, and for moving saidsecond electrode into electrical contact with the terminal; means forvibrating said first electrode while it presses the wire against theterminal to remove insulation on the wire and thereby establish anelectrical connection between the first electrode and the terminalthrough the electrical conductor; and power means for applying a weldingpotential between said electrodes while the first electrode presses thewire against the terminal and the second electrode is in electricalcontact with the terminal, to flow a welding current through theelectrical conductor and terminal.
 11. The apparatus described in claim10 wherein: said pressing means presses said first electrode toward saidterminal with a constant force during operation of said vibrating meansand power means.
 12. The apparatus described in claim 10 wherein: saidvibrating means includes a transducer, an electrically conductive memberacoustically coupling the transducer to the first electrode, anoscillator, first and second signal conductors for connecting saidoscillator to said transducer, and a signal switch in series with saidfirst signal conductor; and said power means includes a power switchwhich is closeable to apply said welding potential between theelectrodes: and including means for automatically opening said signalswitch prior to closing said power switch.
 13. In a method of welding anelectrical conductor which is coated with electrical insulatingmaterial, to an electrically conductive terminal by means of a weldingassembly which includes first and second electrodes, the stepscomprising: pressing at least the first electrode towards the terminalso that a portion of the insulation-coated conductor is caught betweenthe first electrode and the terminal; vibrating a ring-shaped transducercoupled to said first electrode while maintaining the first electrodepressed against the insulation-coated conductor to remove the insulationso that the conductor establishes an electrical path between the firstelectrode and the terminal; applying a welding potential between thefirst and second electrodes while the second electrode is electricallycoupled to said terminal and the first electrode is maintained inelectrical contact with the terminal through the wire; and feeding theinsulation-coated conductor through the ring-shaped transducer. 14.Apparatus for through-insulation welding to an electrical terminal, of awire that includes a central conductor and a covering of insulationthereabout, comprising: an electrode with a tip; means for leading thewire across at least a portion of said tip, including walls forming apassageway in the electrode; means for pressIng the electrode towards aterminal so that the electrode presses the wire against the terminal;means for creating vibrations at the region where the wire is pressedbetween the electrode and terminal to remove insulation at the locationsthereat where the central conductor faces the electrode and terminal,including a transducer with a central hole coaxial with said passagewayin said electrode acoustically coupled to said electrode, and anoscillator coupled to said transducer to drive it, said wire extendingthrough said hole in said transducer; and means for establishing awelding potential between said electrode and terminal to flow a currenttherebetween through said central conductor.